For an integrated circuit (IC) to be powered from a single voltage power supply, a bias point is established internal or external to the chip. This may be done inside the IC as, for example, in the TA7630 IC manufactured by the Toshiba Company of Japan. In such a case, the bias voltage is available at a pin of the chip for coupling thereto a large filter capacitor since it is not practicable to put large capacitors within the circuit housing. In the alternative, the bias can be established external to the IC by an external resistor divider or zener diode circuits, as with respect to the TA9187 chip also manufactured by the Toshiba Company of Japan. Because of different IC designs, and IC to IC variations and other component tolerances, a tolerance in the magnitude of the bias voltage is to be expected. Because of this tolerance in the bias voltage, coupling capacitors are used to block this DC component from coupling between chips to prevent the difference tolerance voltage from being amplified. It is also necessary to filter each bias supply to eliminate crosstalk or feedback within the chip.
It is a common practice in integrated circuits, including integrated circuits having a bias supply generated internal to the IC, for providing bias to individual amplifier portions disposed within the same IC. In such a case, the bias supply and the individual portions within the chip are designed to operate with each other without signal coupling capacitors. In such a case, precautions are taken in the design of the chip to assure this compatibility within the chip. This is not the case for whole discrete IC's which can be operated along with other chips over which the IC designer has no control over.
Since the IC designer has no control over other external chips the specific IC will be used with, bias compatibility with other chips is not a design consideration. For such a case, the data sheets and applications notes for the IC chips specify that decoupling capacitors be used in the signal path and that there be isolation between bias supplies. This is done to assure that the specific IC chip will function as intended and as specified in the data sheets.
Some examples of IC's which provide an internal bias to individual portions within the same housing are shown in the RCA Integrated Circuits for Linear Applications Databook, copyrighted 1986 by the RCA Corporation, U.S.A. In particular, the block diagram of the CA3060 Operational Transconductance Amplifier Array shows three operational amplifiers with a bias regulator. The circuit for a tri-level comparator circuit shows each of the three operational amplifiers receiving bias from the bias regulator. A similar situation is shown in block diagrams for the CA3401, CA3450, CA3493, and CA5422 integrated circuits, and an applications note for the CA3130, all of which show operational amplifiers on the same chip receiving bias from a common bias network also on the chip and receiving power from the V+ terminal.
The present invention recognizes that if all discrete IC's were to operate with the same bias level, e.g. 1/2 of the same supply voltage which is coupled to some or all of the chips in a television receiver or the like, it would be possible to couple the bias/filter points together and force all of the IC's to be coupled to the same bias voltage. This would allow the discrete IC's to have the signal leads DC coupled and to eliminate the AC coupling capacitors otherwise required for coupling signal between chips. Additionally, the individual bias bypass capacitors required for each IC would not be required. Accordingly, it is desired to be able to eliminate signal coupling capacitors otherwise required between discrete IC's and to eliminate the individual bias bypass capacitors otherwise required for the discrete IC's.
As used herein, the terms discrete IC's and chips are intended to include monolithic circuits as well as non-monolithic circuits such as hybrid IC's and encapsulated modules.